GS1100E High Speed instability

[twr1776]

Todd, I agree with the opinions to check EVERYTHING mentioned. The two things I would not bother checking is the fork springs and shocks. If they are OEM you should just junk them for new ones. Yes it is not cheap but for about $ 300 you can get a good set of replacements fronk and back. Do you have any kind of shield on it? An improperly angled or lined up shield can also cause head shake. I found this out the hard way but fortunately was able to keep the bike under control and after lining it up correctly and changing the angle, problem solved.

[bonanzadave]

Last time I mentioned tank slapper here I got crucified . When my bike was new I could roll the throttle for five miles and it was as solid as a rock. After about 20K miles it would get loose at triple digits. I did everything mentioned (except tires) and it got much better. Tires are next. I lived with it for a few years and managed the control by gradually decelerating and pulling down on the bars. I think this may have been a factor of the loose steering bearings. Not a good feeling. Now its got All Balls, Progressive and swing arm bearings. After the tires my next fix will be keeping it below 100mph .

[TheCafeKid]

Is this a good method to control a tank slapper situation? Haven't experienced one myself, but a friend with a highly modded GS1100 did, probably because the geometry was altered considerably from stock. For most riders, they seem to begin when the the throttle is abruptly chopped after accelerating to high speeds (over 140 mph, in his case), and he was able to regain control by getting back on the gas, unloading the front wheel. Haven't heard about letting go of the bars, but yes, that would not come naturally at those speeds.
Tony.

Well, Its worked for me I rode dirt for years and years, and most of the tank slappers I have experienced werent at tripple digit speeds to say the least. The way I have always understood the dreaded tankslapper is this: the more you fight the bars to get them under control, the worse the bike fights you back. Most of the 'slappers ive experienced started one of two ways; The front wheel, once airbourne, came down out of line with the rear wheel, and the bike, under power, wants to straighten itself out simply because of the physics of a motorcycle. So, the bars jerk one direction or the other. The problem begins when the throttle either gets slapped shut, or wacked open. This doesnt seem like a big deal just reading it, but it generally happens so fast, your first instinct is to jerk the bars back, thus doing the opposite to the throttle that the bike did to you. This starts a chain reaction, an almost hobby horse effect, the CG keeps shifting from front to back as the throttle comes on and off, the bike keeps trying to right itself, and you, in essence, are fighting it. Because the bike, naturally while in motion, wants to go straight, and upright, I was always taught to just let go, just for a second. The bike will right itself. Now, this may not be the true definition of a "tankslapper" but the action pretty much resembles exactly what happens in a high speed tank slapper.

The scariest time it ever happened to me was a couple years ago in Elkins, WV. I was out there with Steve and the Goldwing group, and we were leaving the hotel that morning to start the days ride. The group leaders had blocked traffic coming from the left, so our group could pull out of the motel parking lot. But no one had stopped it coming from the right. Some jerk in an SUV decided he didnt possibly have the time to wait for our 10 or so bikes to pull out, so he tried to cut into the line of bikes right as I was rolling thru the median. He was gonna mow me down more or less. So i goosed the throttle to get the hell out of his way. Well at the time I didnt know what had really happened, but as soon as I goosed it, the front wheel came up just a bit (i was cresting a hill) and when it came back down the bars went buck crazy.. they slammed hard left, then back to the right, and back and forth. After probably the third time it jerked my arms, i just let go. It wasnt really a concious descision, just wrote memorization I suppose. But I let go. Just for a second. And the bars jerked back to the left hard, and then came back to center and I was going straight again. I gave her some throttle and booked it out of his way. At first, I was ticked at myself, cause I thought it was my fault for jumping on the throttle first thing in the morning on cold cold tires. But i found out at our first stop that the person behind me saw everything. She asked how I managed not to go down. I said that I really didnt know, I thought that I was going to to be honest. I had apparently ran through a patch of asphault coloured sand more or less, and when I goosed it, the rear tire gripped hard at first, and once it got into the sand it busted loose and she said the bike looked like i was on a bucking bronco. the front end was going one way, and the rear end the other. That was pretty damn butt puckering I can say that... But, I didnt go down, and I figure if I had hung on, and fought the bars, I probably would have.

Sorry for the long 'jack

[teddux]

...replace the fork oil too. That should be done every season or two if you really put miles on your bike. Also if you haven't replaced the oil already, I would suggest it simply because an imbalance of Less than a milliliter, according to the shop manual, will also cause

On my Nighthawk, a simple "imbalance" of air pressure IN FORKS would cause this.

[TheCafeKid]

On my Nighthawk, a simple "imbalance" of air pressure IN FORKS would cause this.

Yeah, Im not sure how much i believe this.. But, if they saw fit to print it, It probably should be taken into consideration. The manual states that improper oil or air levels in the forks, or uneven levels, will cause stress on the axle, stress on the fork walls, yadda yadda yadda. I measured carefully, but Im sure its not EXACTLY even. Ive never had a problem, but I do try VERY hard to follow their suggestions..

[tfb]

My '82 Katana was getting the wallows through fast sweeping bends, certainly a bit disconcerting at (an indicated) 140kph = 87mph.

Got home and checked out my running gear. Here's what I found:
1. Front tyre worn out. Not going to help.
2. Front wheel bearings with freeplay. Bad.
3. Damping pistons in (rebuildable IKON) rear shockies scored, one much more scored than the other.
4. Swingarm bearings & bushes past their best, with visible scoring marks on the bushes.

So I went and fixed all that, and put new oil in the front forks while I was at it.

All is now well; I can push the old warhorse into fairly rough bends with a lot more confidence.

In addition, as a number of folks have already mentioned, make sure that your wheels are aligned. Do not trust the gradation marks on the swingarm for this; they are usually a mile out. Use a straight edge.

[Nessism]

Checking the wheel alignment using the string method is a simple way to determine if the wheels are in the same plane. Once you have the wheels aligned, take note of where the adjusters fall relative to the marks on the swingarm - if they are off you need to keep this in mind for when you do subsuquent adjustments for chain tension.

Regarding the alignment being off from the factory, my understanding is that some racers from back in the day used to check and adjust their brand new bikes to make sure everything was honky dory before they hit the track. It was not unusual for the bikes to be off to some extent from new but I can't quantity how much.

[tfb]

It was not unusual for the bikes to be off to some extent from new but I can't quantity how much.

For the record, the gradations on my Katana's swingarm are a full 1 1/2 marks out of whack. I think that's a scary degree of inaccuracy.

[Baatfam]

Yeah, Im not sure how much i believe this.. But, if they saw fit to print it, It probably should be taken into consideration. The manual states that improper oil or air levels in the forks, or uneven levels, will cause stress on the axle, stress on the fork walls, yadda yadda yadda. I measured carefully, but Im sure its not EXACTLY even. Ive never had a problem, but I do try VERY hard to follow their suggestions..

Yes, I also wonder about this...and I tried really hard to get the levels right when I just rebuilt the forks...but....
Last summer I had a leaky seal, and when I finally tore down the forks that side was near empty, while the other wasn't and never notice anything uneven...

As long as there is enough oil to work the dampeners and such inside, I can't imagine a few millimeters of height difference would effect much.
Maybe slightly more air compression space...

[bonanzadave]

Checking the wheel alignment using the string method is a simple way to determine if the wheels are in the same plane.

I know HDs were built with wheel offset. Have we determined if the GSs had any ? I have two 8' straight edges and I swear I have near a 1/4" offset front to back.

[Nessism]

I know HDs were built with wheel offset. Have we determined if the GSs had any ? I have two 8' straight edges and I swear I have near a 1/4" offset front to back.

I'm not aware of a factory offset on GS bikes. In fact, some of the factory service manuals show the string method to check alignment and there is no mention about offset.

[Mysuzyq]

I know HDs were built with wheel offset. Have we determined if the GSs had any ? I have two 8' straight edges and I swear I have near a 1/4" offset front to back.

No Dave, that is not by design. You may have found the root of your handling issues, if that reading is accurate.
Tony.

[bonanzadave]

You may have found the root of your handling issues, if that reading is accurate.

I was as exacting as possible. Made cutouts on my straight edges to clear the centerstand. Used a case of pop cans to raise the straight edges off the ground. Got down to 1/16" turns on the adjusters and that was as close as I could get. This was before the head bearing change so I have to check again. Any chance the tires could have that much error ?

[Mysuzyq]

I would check again if you've made changes since that reading, though I'm not sure if head bearings alone could account for it. IIRC, Posplayr had made some observations re. tires and the effect on alignment readings.....maybe he'll chime in with some input.
Tony.

[posplayr]

I would check again if you've made changes since that reading, though I'm not sure if head bearings alone could account for it. IIRC, Posplayr had made some observations re. tires and the effect on alignment readings.....maybe he'll chime in with some input.
Tony.

Chime

http://www.thegsresources.com/_forum/showpost.php?p=1159228&postcount=16

http://www.thegsresources.com/_forum/showpost.php?p=1102275&postcount=4